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Publication numberUSRE11865 E
Publication typeGrant
Publication dateOct 23, 1900
Publication numberUS RE11865 E, US RE11865E, US-E-RE11865, USRE11865 E, USRE11865E
InventorsNikola Tesla
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Nikola tksl a
US RE11865 E
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Description  (OCR text may contain errors)

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' (Applicltion filed Sept. 21, 1900.)

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SPECIFICATION forming part of Reissued Letters Patent No. 11,865 dated October 23, 1900.

Original No. 665,838, dated August 14, 1900. Application for reissue filed September 21, 1900- Berill No. 30 722.

To all whom it may concern.-

Beit known that I, NIKOLA TESLA, acitizen of the United States, residing in the borough of Manhattan, in the city, connty, and State of New York, have'invented certain new and useful Improvements in Methods of Insulating Electric Conductors, of which the following is a specification, reference being bad to the accompanying drawings.

It has long been known that'*;many sub stances which are more or less conducting when in the fluid condition becomejnsulators when solidified. Thus water, which is in a'measure conducting, acquires insulating properties when converted into ice. The existing information on this subject, however, has been heretofore of a. general nature only and chiefly derived from the original observa t-ions of Faraday, wh'o estimated that the substances upon which he experimented, such as water and aqueous solutions, insulate an electrically-charged conductor about one hundred times better when rendered solid by freezing, and no attempt has been made to improve the quality of the insulation obtained by this means or to practically utilize it for such purposes as are contemplated in my present invention. In theconrse of my own investigations, moreespeciall y those of the electric properties of ice, I have discovered some novel and important facts, of which the more prominent are the following: first, that under certain conditions, when the leakage of the electric charge ordinarily taking place 'is. rigorously prevented, ice proves itself to be a much better insulator than has heretofore appeared; second, that its insulating properties may be still further improvedby the addition cf other bodies to the water; third,that the dielectric strength of ice or other frozen.

aqueous substance increases with the reduct-ion'of temperature and corresponding increase of hardness, and, fourth, that these bodies afford a still more effective insulation for conductors carryingintermittent or alternating currents, particularly of'high rates,

surprisingly-thin layers of ice being capable of withstanding electromoti've forces of many hu ndrcds and even thousands of volts. These and other observations have led me to their:- vention of a novel method of insulating con- 7 above facts and advantageous in the utilization of electrical energy for industrial and commercial purposes.

This method consists in insulating an electric conductor by freezing Orsolidifyiugand maintaining in such state the material surrounding or contiguous to the conductor, using for the purpose a gaseous cooling agent circulating through one or more suitable channels extending through or in proximity to the said material.

Iii the practical carrying out of my method I may employ a hollow conductor and pass the cooling agent through the same, thus freezing the water or other medium in contact with or close to such conductor, or may use expressly for the circulation of the cooling agent an independent chan'neland freeze or solidify the adjacent substance in which any number of conductors may be embedded. The conductors may be'bare or covered with some material which is capable of keeping them insulated when it is frozen or solidified.

The frozen mass may be in direct touch with the surrounding medium, or it may be'in a degree protected from contact with the same by I an inclosure more or less impervious to heat. The cooling agent may be any kind of gas, as atmospheric air,'oxygen, carbonic acid, ammonia, illuminating-gas, or hydrogen. It may be forced through the channel by pressure or suction produced mechanically or otherwise.

It may be continually renewed or indefinitely used, being driven back and forthor steadily section, or partlysmconstructive details to be described.

InjFi'g. I, C is a hollow conductor, such'as a steel tube, laid infu. body of water and communicating with a'reser'voir 1'', butelect rically insulated from the same atj. A pump or compressor p, of any suitable construction, connects r with another similar tank r, productors, rendered practicable by reason oftlie l vided with an inlet-valve '0' The air or other 2 11,ses

gas which is used as the cooling'agententering through the valve-1: is drawn through the tank 'r'and pu m p 1) into the reservoirr', escaping thence through the-conductor C- under any desired pressure which may be regulated by a valve 1;. Both the reservoirs r and r" are kept at a low temperature by suitable means, as by coils or tubes t t and t 5, through which any kind of refrigerating fluid may be circulated, some provision being preferably madefor adj listing the flow of the same, as by valves-v. I The gas continuously passing through the tube or conductor 0 beingvery cold will freeze and maintain in this state the water in contact with or adjacent to the conductor and so insulate it. Flanged bushin gs i 1?. of non-cond noting materialnnay be used'to prevent the leakage ofthe current which would otherwise occur, owing to the formation of a superficial film of moisture overthe ice projectingout of the water. The tube being kept insulated bythis means may then be employed in'zthemanner of an ordinary telegraphic orherjcable by connecting either or bothvof ftb ie-terminals b b in a eir'cui tjincluding theearth.

. Inf na'ny cases icw beef advantage to cover the hollowcondnctofr with a thick layer of some cheap material, as felt, this beinginqdicated by (J in Fig.2. Such-. a covering,

penetrable' by water, would be ordinarily. of littleorno use; but whenembedded in the ice i't-iinprovesthe insulating qualities of the 'jsame. In this instance it furthermore serves 5 tog'restly reduce the quantity of ice required, rate-of melting, and thefinllux of heat waffrom the outside,'t-h'us diminishing the ex- -;f-penditurefo'f energy necessary for the maintenauce of normal working conditions. As -,o regards this energy and other; particulars of I [importance they will varyaccording to the special demands in each case.

Generally considered,the'cooling agent will have to carry away heat at a rate suflicient to keep the conductor at the desired tetn perature and to maintain a layerfof the required thickness of the substancesurrounding it in a frozen state, compensatingcontinually for theheat flowing in through the layer and wall so of the conductor and that generated by mechanical and electrical friction. To meet these conditions, its cooling capacity, which s dependent on the temperature, density,

-.velocity,and specific heat,will be calculated 5'5 the help of data and formulae familiar to engineers.

fo' r- .'the use contemplated; but in exceptional nstances some other gas, as hydrogen, may be resorted to, which will permit a much 6ogreater rate of cooling and a lower temperatnre to be reached. Obviously whichever be employed it should before entering the hollow conductor or channel be thoroughly dried and separated from-all which bycon- 'densa tion and deposition-or otherwise might 1 cause an obstruction to its passage. For these purposes apparatus may employed tricity for ind nstrial Air will be, as a'rule, suitable: "plan.

which is well known and which it is unnec essary to show in detail. I

Instead of being wasted at the distant sta- 10 tion the cooling agent maybe turned to some profitable use. Evidently in the industrial and commercial exploitation of my invention any kind of cooling agent capable of meeting the requirements maybe conveyed from one to another station ,and there utilized for refrigeration, power, boating, lighting, sanitation, chemical processes, or any other purpose to which it maylenditself, and thus the revenue of the plant may be increased.

H As to the temperatnreof the conductor, it will be determined by the nature of its use and considerations of economy. Forinstance, if it be employed for the transmission of telegraphic messages, when the loss in electrical friction may be of no consequence, a very low temperature may not be required; but if it be used for transmitting large amounts of electrical energy, when the frictional waste may be a serious drawback, it will be desiro able to keep it extremely cold. The attainmentof this object will be facilitated by any provision for reducing as much as possible the flowing in of the heat from the surround ing medium. Clearly the lower the temperatnre of the conductor the smaller will be the loss in electrical friction; but, on the other hand, the colder "the conductor the greater will be the influx of heat from the outside and the cost of cooling agent.

From such I00 and similar considerations the temperature secnring'the highest economy will be ascertained.

Most frequently in the distribution of elecnrposes, as in my sys- :05 tom of power transmission by alternate currents, more than one conductor will be required, and in such cases it may be convenient to circulate the cooling agentin a closed path formed by the conductors A plan of I to this kindis illustrated in Fig. 3, in which 0' and 0 represent two hollow conductors embedded in a frozen mass underground and communicating, respectively; with thereservoirs R and R", which'are connected bya re- 1'15 ciprocating or other suitable pu'm'p P. Cooling coils or tubes T' T and 'l T, with regulating-valves 'v"v" are employed, which are' similar to and 'serve the same purpose as those shown in Fig. 1. Other features of m similarity, though unnecessary,|ns.- 4:. trat-ed to facilitate an understanding of the A three-way valve V, is provided, which when placed with its lever 1 as indicated allows the cooling agent to enter 1:; through the tubes u u"' and pump P, thus filling the reservoirs R R. and hollow con, ductors .C C; but when turned ninety degrees the valve-shuts off the communication .to the outside through the tube to and estab- 13c lishee a connection between the reservoir R.

and pump P through the tubes 11. and u, thus permitting the cooling agent to be circulated in the closed path 0' C R u-n' I R by the necting the conductors to the circuit at each station.

In laying the conductors, as 0' 0 whatever be their number,.a-trench will generally be dug and a trough, round or square, as T, 0! smaller dimensionsthan the trench, placed in the same, the intervening space being packed with some material (designated by M M M) more or less impervious to heat,

as sawdust, ashes, or the like, Next the con-' doctors will be put in position and temporarily supported in any convenient manner,

and, finally, the trough will be filled with first-er or other substance W, which will be gradually frozen by circulating the cooling agent in the closed path, as before described. .Usually the trench will not be-level, but will follow the undulations of the ground, and this will make it necessary to subdivide the trough in sections or to effect the freezing of the substance filling it successivelyin parts. This being done and "the conductors thus insulated and-fixed, a layer of the same or similar material M M M will .be placedon the top and the whole covered with earth or.

pavement. The trough may be of metal, as

sheet-iron, and in caseswhere the ground is used as the return-circuit it may serve as a main, or it may be of any kind of material more or less insulating. :Figs; 4 and 5 illustrate in crosssection two such under-- ground troughs '1" and T", of sheet metal,

with their adiathermanousinclosures, (designated M and M", respectively,) each trough containing a single central hollow conductor, as O O. In the first case the insulation W is supposed to'be ice obtained by freezing water preferably freed of air in order to exclude the formation ot'dangerous bubbles or cavities while in the second case the frozen mass W is some aqueous or other substance or mixture highly insulating when in this condition.

It should be stated that in many instances it may be practicable to dispense with a trough by resorting to simple expedients in the placing and insulating of the conductors. In fact, for some purposes it may be sufiicien t to simply cover the latte} with a moist mass, as cement or other'plastic material, which so long as it is kept at a very low temperature and frozen hard will' afford adequate insula tion.

Another typical way of carrying out my invention, to which reference has already been made, is shown in Fig. 6, which represents the cross-section of a trough, the same in other respects as those before shown, but containing instead of a hollow conductor any kind of pipe or conduit. L. The cooling agent may be driven in any convenient manner through the pipe for the purpose of freezing the wateror other substance filling the trough, thus insulating and fixing a number of conductors cc 0. Such a plan may be particularly suitable in cities for insulating and fixing telegraph and telephone wires or the like. In such cases an exceedingly-low temperatu-re of the cooling agent may not be-required, and the insulation will-be obtained at, the expense of little power. The conduit L may, however, be used simultaneously for conveying and distributing any kind of gaseous cooling agent for which th'er'isa demand through the district. Obviously'two'such con similar du its may be provided and used in a mannerv as the conductors C 0. g

It will often-be desirable to place in the saine trough a great number of wires or conduct-ore serving for a variety of purposes. In such acase a plan may be adopted which is .-illustrated in Fig. 7, showing a trough similar-- to that in Fig. 6 'with the conductors in cross-section. The cooling agent maybe in this instance circulated, as in Fig. 3 or otherwis'e, through the two hollow conductors (3 and C, which if found-advantageous may be covered with a layer of cheap material 01pm, such as will improve theirinsulation, but not. preventthe freezing or solidification of the surroundingsubstance W. The tubular-conductors C 0, preferably of iron, may then serve to con vey heavy currents for supplying light and power,while the smallones c c' o embedded in the ice or frozen mass, may be usedtor any oth'erpurposes.

.While my invention contemplates, chiefly, the insulation of conductors employed in the transmission of electrical. energy to a distance, it may he, obviously, otherwise usefully applied. In some'instances, for example, it may be desirable to insulate and sup port va conductor in places as is ordinarily done by means of glass or porcelain insulators. This may be eflfected in many ways by conveying a cooling agent either through the conductor-or through an independent channel and'freez'ing or solidifying any kind of substance, thus enabling it to serve the purpose. Such an artificial insulating-support.- is illustrated in Fig. 8, in which a represents avessel filled with water or other substance to, frozen by the agent circulating through the hollow contiuctor C", which is thus insu- To improve the insulated and supported. lation on the top, where it is most liable to give way, a layer of some substance w, as oil, may be used, and the conductor may be covered near the support with insulation 11 i, as shown, the same extending into the oil, for reasons well understood.

Another typical application of my invenondary conductors, bare or insulated, of a transformer, which are wound on a core N and immersed in water or other substance W,

contained in a jar; II, and, as before stated,

convenient manner, as through the hollow primary I", for the purpose of freezing the substance W. Flanged bushings'rl d and oilcupsee, extending into the frozen mass, illustrate suitable means for insulating the ends ofthe two conductors and preventing the leakage of the currents, A transformer as described is especially fitted for use with currents of high frequency when a low temperature of the conductors is particularly desirable, and ice affords an exceptionally-effect.- ive insulation.

It will be understood that my in vcntion may be applied in many otherways, that the speclal means here described will be greatly varied according to the necessities, and that in each case many expedients will be adopted which are well known to engineers and electricians and on "which it is unnecessary to dwell. However, it may be useful to state that in some instances a special provision will haveto be made for effect-ing a uniform cooling of the substance surrounding the conductor-throughout its length. Assuming in Fig. 1 the cooling agent to escape at the distant end freely into the atmosphere or into a reservoirmaintained at low pressure, it wil in passing through the hollow conductor 0 move with a velocity steadilyincreasing toward the end, expanding isothermally,or nearly so, and

,hence it will cause an approximately-uniform formation of ice along the conductor. In the plan illustrated in Fig. 3 a similar result will be in a measure attained, owing to the compensating effect of the hollow conductor C and O, which may be still further enhanced by reversing periodically the direction of the flow in any convenient manner; but in many cases special arrangements will have to be employed to render the cooling more or less uniform. 5, and 6, instead of a single channel two concentric channels L and L may be provided and the cooling agen t passed through one and returned through the other, as indicated, diagrammatically, in Fig. 10. In this and any similar arrangement when the flow takes place in opposite directions the object aimed atwill be more completely attained by reducing the temperature of the circulating cooling agent at the distant station, which may be done by simply expanding it into a large reservoir, as R", or cooling it by means of a tube or coil '1 or otherwise. Evidently in'the case illustrated the concentric tubes may be used as independent conductors if insulated from each other and from the ground by the frozen or solidified substance.

Generally in the transmission of electrical For instance, referring to Figs. 4,

conveyed. 'In such cases a fairly-uniform freezing of the insulating substance will be attained without difficulty by the c0mpensating cfIe-et of the oppositely-circulating cooling agents. In large plants of this kind when the saving of electrical energy in the transmission is the most important considerv ation or when the chief object is to reduce the cost of the mains by the employment of cheap metal, as iron or otherwise, every effort will be made to maintain the conductors at the lowestpossible temperature, and well- 'known refrigerating processes, as those based on the regenerative principle, may be resorted to, and in this and any other case thehollow conductors orchannelsinstead of merely serving the purpose of conveying the cooling agent.

may themselves form active parts of the refrigerating apparatus.

From the above description it will be readily seen that my invention forms a fundamental departure in the principle from'the established methods of insulating conductors employed'in the industrial and commercial application of electricity. It aims, broadly, at

obtaining insulation by the continuous ex-,

penditure of a moderate amount of energy instead of securing it only by virtue of an in- .herent physical property of the material used More especially, its object is as heretofore. to provide, whenand wherever required, insulation of high ,quality, of any desired thickness, and exceptionally cheap,'and to enable the transmission of electrical energy under conditions of economy heretofore unattain-' able and at distances until now impracticable by dispensing with the necessity of using costly conductors and insulators.

What I'claim as my invention is- 1. The method of insulating electric conductorsherein described which consists in imparting insulatingproperties to material surrounding or contiguous to the said conductor by the continued action thereon of a gaseouscooling agent, as set-forth.

Q2. The method of insulating electric condoctors herein described which consists in reducing to and maintaining in a frozen or 'solidlfied condition the material surrounding or contiguous to the said conductor by the action thereon of a gaseous coolingagent maintained in circulation through o'ne or more channels as set forth,

3. The method of insulating electric conductors herein described which consists in surrounding or supporting the conductor by r when in a frozen or solidified state, and main- 11,ses 5 mining 'the material in such a state by the circulation through one or more channels extending through it of a gaseous cooling agent, as set forth.

4. The method of insulating an electric cond uctor which consists in surrounding or supporting -said conductor by a materialwhich acquires insulating properties when frozen or solidified, and maintaining the material in such state by passing a gaseous cooling agent continuously through a channel in said conductor, as set forth.

5. The method of insulating electric conductors, which consists in surronnding'or su pporting the said conductors by a material which acq uires insulating properties when in a frozen or solidified state, and maintaining the material in such state by the continued application thereto of a gaseous cooling agent, asset forth.

6. The'method of insulating conductors herein set forth which consists in surrounding or supporting the conductors by a material which acquires insulating properties when in a frozen orsolidified state, and maintaining the material in such state by the circulation of a gaseous cooling agent through a circuit of pipes or tubes extending through the said material as set forth.

7. The method of insulating electric conductors which consists in laying or supportr ing the conductors inst-rough or conduit filling the trough with a nialerial which acquires insulating properties when frozen or solidi-- as to freeze or solidify the material, as set forth.

a 8. The method -of insulating electric cond uctors which consists in embedding the same in a moist or plastic compound which acquires insulating properties when in a frozen or solidified state, and maintaining the compound in such state by circulatinga gaseous cooling agent through one or more channels extending through the compoundfas set forth.

9. The method of insulating electric conductors which consists in laying or support mg the conductors in a trough or conduit, filling the trough with a material which acquires insulating properties when frozen or solidifled, protecting the trough from the surround-. ing medium in which it is laid by an adiathermanonsinclosure, and then freezing or solidifying the-material surrounding the con.-

ductors and maintaining the same in such. state by circulating a gaseous cooling agent.

through one or more channels. extending through the same, as set forth.

v NIKOLA TESLA. Witnesses:


Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2439592 *Feb 25, 1943Apr 13, 1948Ljuslin Lindstrom Dag ViktorMethod of temporarily repairing electric cables damaged by moisture
US2686215 *Dec 12, 1950Aug 10, 1954Bell Telephone Labor IncIsothermal electric cable